Magnetic core



Oct. 12, 1965 T. J. TWOMEY 3,212,042

MAGNETIC CORE Filed Nov. 28, 1962 Moms J 746mg, y fiM/F 227:

HA? uW/dmg.

United States Patent 3,212,042 MAGNETIC CORE Thomas J. Twomey, Rome, Ga., assignor to General Electric Company, a corporation of New York Filed Nov. 28, 1962, Ser. No. 240,692 3 Claims. (Cl. 336-217) This invention relates to magnetic cores and more particularly to improvements in laminated flat stacked three legged magnetic cores for core type, as distinguished from shell type, stationary three-phase alternating current electrical induction apparatus.

Such cores are characterized by two alternated or interleaved sets of layers which may respectively be referred to for convenience as a set of odd numbered layers and a set of even numbered layers although it makes no difference which set is which.

Each layer in each said set of layers is generally made up of several identical sheets of laminations. The reason for using more than one sheet per layer is that it reduces the amount of labor involved in laying up or stacking the core. Each sheet of laminations often has seven separate pieces of magnetic material, there being three parallel coplanar equally spaced leg pieces and four yoke pieces extending perpendicular to the leg pieces and joining the corresponding ends of adjacent pairs thereof. As a consequence of this construction each sheet also has eight butt joints between adjoining ends of leg and yoke pieces, the two joints at each end of the center leg being referred to collectively as a T-joint and the other four joints being called corner joints.

In order to reduce the magnetic reluctance of such a core the corresponding joints in adjacent layers are staggered or offset from each other in the direction of magnetic flux therethrough so as to produce an area of overlap. Because the magnetic pieces making up each sheet are generally made of highly grain-oriented cold-rolled silicon alloy steel cut to length from a rolled or coiled strip of such material they have a most favorable magnetic direction corresponding to their lengthwise direction which is also the normal direction of magnetic flux therethrough. This staggering or offsetting of the joints can be accomplished by making the sheets of the layers of one set different from the sheets of the layers of the other set.

In order to minimize deviation of the direction of flux in the pieces from their most favorable magnetic direction when flux goes around a corner the joints are usually so called mitre joints. There has always been a problem with T-joints because magnetic flux not only enters and leaves the vertical leg of the T in both directions in going from and to both outer legs, but it also goes directly through the horizontal top arm of the T in going between the outer legs. In other words, while the mitre joint is admirably suited to the corner joints, it is not as well suited to the T-joints.

Another problem with such cores is that of waste of material in cutting the parts particularly at the T-joints. This problem of scrap is accentuated by the relatively high price or cost of the material.

Another problem is complexity and high cost of machinery for producing such parts.

A further problem with such cores is the substantial number of different parts which are required.

Accordingly, it is one object of my invention to minimize the number of different lamination patterns utilized in a three-legged stacked magnetic core formed of grainoriented magnetic strip material.

It is a further object of my invention to form a threelegged magnetic core of congruent lamination layers each made up of a small number of different lamination patterns which are so mitred and notched to provide offset mitred joints that they are individually symmetrical about their transverse axes and may be cut from a strip material of uniform width without waste and with a minimum number of different angular par-ting dies.

It is still another object of my invention to provide a three-legged magnetic core of grain-oriented magnetizable material wherein each lamination sheet is formed of seven separate pieces shaped in a lesser number of different patterns to minimize cutting waste and yet maximize the number of offset mitred joints in the core.

In accordance with the present invention, there is provided a novel three-legged magnetic core made up of several sheets of laminations wherein each sheet is composed of lamination pieces in only three different patterns. In a preferred embodiment each sheet contains seven different lamination pieces but only three different shapes or patterns in that the leg pattern is in triplicate constituting three identical leg pieces, one yoke pattern is in duplicate constituting two identical yoke pieces, and the other yoke pattern is in duplicate constituting the remaining two identical yoke pieces. While the three patterns are different in the sheets of adjacent layers, i.e. in the different sets of layers, there is a total of only six different lamination patterns in the entire core. Each of the six differently shaped parts or patterns is cut at 45 to provide mitre core joints and notched at the mitred ends to provide offset joint overlay between the layers. The notches are so located that each lamination piece having both ends mitred is symmetrical about its own central transverse axis. By this arrangement all notches are lo cated on the same side of center in a continuous strip cutting operation thereby to minimize waste and to minimize the number of different parting dies required in manufacture.

In my improved structure the T-joints at opposite ends of the center core leg form a mitre butt joint with the yoke piece at one side and a square butt joint with the oppositely extending yoke piece. The four corner joints are all mitred so that in each lamination sheet six of the eight joints :are mitred. For this reason my core is referred to herein as a three-quarter mitre joint core. The lamination pieces are each symmetrically offset from the corner diagonal at their mitred ends so that the corner joints overlap between layers and alternate asymmetry of the T-joints in adjacent layers is accomplished with no waste when cutting from continuous strip material.

Another feature of the invention is that although the T-joints are quite asymmetrical in the individual sheets and layers, the asymmetry is reversed in adjacent layers so that the T-joints of the core are balanced or magnetically symmetrical.

A further feature of the invention is that the individual sheets are asymmetrical about the longitudinal center line of their center legs, but the asymmetry is reversed in adjacent layers so that the core as a whole is balanced or symmetrical.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing,

FIGURE 1 is a perspective view of a core in accordance with the present invention, the front sheet being of one of the odd numbered set of layers, while FIGURE 2 shows a sheet of the even numbered set of layers which has been slid downward out of the core shown in FIG- URE 1 in order to show the details of its construction.

Referring now to the drawing and more particularly to FIGURE 1, there is shown therein a fiat stacked laminated magnetic core 1 having a thickness or build 2 which is determined by the number of lamination layers therein. These lamination layers are divided into a set L of odd numbered layers of which the single exposed sheet S on top or in front at FIGURE 1 is representative, and a set L of specifically different even numbered layers of which the single sheet S shown exposed at FIG- URE 2 is representative, it being understood that the layer of FIGURE 2 underlies the top or outer layer in FIGURE 1 and has been slid downward out of the core in order to show its details.

All of the layers are geometrically congruent or edgewise coincident in the sense that neither set has either projections which stick out beyond the other set, or voids or recesses which do not extend out to the edge of the other set.

In order to simplify the assembly of the core by reducing the number of different operations or steps involved, each layer of laminations usually consist of more than one duplicate sheet of lamination. The presently preferred arrangement is two sheets per layer, although it will be understood that there can be N sheets per layer where N is any integer from one to nine.

Referring now to the sheet S shown in detail in FIG- URE 1, it comprises a center leg piece 3 and two outer leg pieces 4 and 5 which are identical and constitute a single leg lamination pattern A in triplicate. As shown, the ends of these pieces or this part are beveled or mitre cut at an angle of 45 degrees to their lengthwise dimension with the end tips or points cut off to produce square corners on the same side as indicated at 6 on piece 5. This sheet also comprises two yoke pieces 7 and 8 which are identical and consist of a duplicated yoke lamination pattern B. These also have their ends mitred or beveled cut at an angle of 45' degrees to their lengthwise dimension except that those bevel cuts are square notched on the same side of the piece or part as indicated at 9 on piece 7 so that the cuts do not extend in a straight line entirely across the ends of the pieces.

The sheet S also comprises two yoke pieces 10 and 11 which are duplicates of a common lamination pattern C, one end of which is square cut and the other end of which is 45 degree beveled or mitre cut except that it has a notch corresponding to the notch 9 of pattern B. The depth of the notches 9 is equal to the width of the tips of the leg patterns A which have been cut off to make the square ends or corners 6 so that not only do the ends of the leg and yoke patterns interfit without gaps between them when assembled as shown in the drawing so as to make right angle 45 degree mitre joints, but they also interfit when one of the pieces is rotated about its longitudinal axis 180 degrees and aligned with another piece. In other words, the pieces can all be cut from a strip of material without waste or scrap by using a shear or a parting die with angularly extending portions, the major portion of which is at 45 degrees to the longitudinal axis of the strip and a shorter portion of which is perpendicular thereto so as to produce the squared off ends 6 and notches 9 of sequentially cut pieces in a single shearing operation. It will be observed in FIGURE 1 that there are four mitre corner joints and two T joints at opposite ends of the center leg 3 respectively, and that the T joints are a symmetrical in that they are mitre butt joints on the right-hand side and square butt joints on the left-hand side.

Referring now to the sheet S shown at FIGURE 2, its center leg 12 and outer legs 13 and 14 are identical and consist of a leg lamination pattern X in triplicate which however. is different from pattern A in that it is shorter and instead of having square cut ends 6 it has notched ends corresponding to the notches 9 of pattern B. In fact, pattern X has the same geometrical shape as pattern B but'is longer. FIGURE 2 also has yoke pieces 15 and 16 comprised of a lamination pattern Y in duplicate, this pattern being longer than its counterpart B and having square cut corners on the same side corresponding to the corners 60f the pattern A. In other. words, the geometr rical shape of pattern Y corresponds to that of pattern A but it is shorter. In addition, there are yoke pieces 17 and 18 comprising a duplicate pattern Z which is the counterpart of pattern C except that instead of having one end notched as pattern C has, it has the tips squared off as at 6 for pattern A.

The sheet S shown in FIGURE 2 not only has closely interfitting mitre butt joints but also its pieces can be cut like the pieces of the sheet in FIGURE 1 from a strip of magnetic material without waste. It will also be observed that its corner joints are offset from a diagonal running from the inner corner point to the outer corner point of the core in opposite directions from the corresponding corner joints of the sheet S in FIGURE 1 so that when the layers (i.e. groups of identical sheets) are interleaved these corner joints are offset in each layer one from the other and provide an area of overlap. Also, in the sheets S of the even numbered layers as shown in FIGURE 2, the square butt joints of the T joints are on the right of the center leg and the degree mitre joints are on the left so that when these T joints are superposed in the core, the core as a whole has magnetically balanced or symmetrical T joints.

While all of the core parts are shown to have equal thickness and width which, of course, will result from their being cut from the same strip of magnetic material this, of course, is not essential and if, for example, it is desired to have a core whose legs are cruciform in cross sec tion so as to provide better space factor in the windows of electrical coils or windings of circular configuration, the core may be built up of sections having different width parts cut, for example, from strips of magnetic of different width as is otherwise common practice in the construction of so-called cruciform cores. However, any such core can be viewed as a plurality of superposed cores shown in FIGURES l and 2 but of progressively dilferent width parts.

It will also be observed that in any piece which has both ends mitred the square cut tip ends or corners 6 or the notches 9, as the case may be, are both on the same side of the piece so that, in other words, its shape is symmetrical about its transverse center line. This structural feature facilitates the indexing or measured cutting operation of the parts so that this indexing or measuring can all be done on the same side of each piece which is an advantage in the precision cutting to length of the individual parts.

While there have been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and therefore it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters' Patent of the United States is:

1. A three-quarter mitre joint magnetic core for threephase electrical induction apparatus comprising, in combination, a plurality ofinterleaved fully congruent lamination layers eachformed of at least one sheet of laminations, each said sheet comprising a center winding leg piece, two outer winding leg pieces, and four yoke pieces joining the ends of adjacent leg-pieces so that there are four corner joints between the outer leg pieces and the yoke pieces and two T-joints each comprising two joints between the center leg piece and two yoke pieces, the T- joints in the odd numbered layers being square butt joints with the adjacent yoke piece on one side of the center leg and mitre butt joints with the adjacent yoke piece on the other side of the center leg, the T-joints in the even numbered layers being mitre butt joints with the adjacent yoke piece on said one side of the center leg and square butt joints with the adjacent yoke piece on said other side of the center leg, all of the corner joints being mitre butt joints whereby three-quarters of the joints in each layer and in the core as a whole are mitred and although the layers are unsymmetrical in the region of their T-joints the core as a whole is symmetrical in the region of its T-joints, the leg pieces of one set of alternate layers all being replicas of the same pattern, the leg pieces of the other set of alternate layers all being replicas of a differ- :ent pattern.

2. A laminated magnetic core for three-phase stationary induction apparatus comprising, in combination, a plurality of congruent fiat stacked layers of N sheets per layer where N is any integer from one to nine, each sheet consisting of seven separate lamination pieces of which three are identical in shape and the other four consist of two differently shaped pairs of two identical pieces so that there are only three differently shaped pieces per sheet, the lamination pieces of the sheets comprising odd numbered layers being different in shape from the lamination pieces of the sheets comprising even numbered layers whereby there is a total of six different lamination patterns in the core, all of said pieces being equal width and equal thickness different length portions of magnetic strip material and having a most favorable magnetic direction coinciding with their lengthwise dimension, each sheet having a center leg piece and two outer leg pieces parallel to and equally spaced from the center leg piece, the leg pieces of the sheets of the odd numbered layers each comprising the first one of said six patterns and the leg pieces of the sheets of the even numbered layers each comprising the second one of said six patterns which is shorter than said first one of said six patterns, each sheet having four yoke pieces extending at right angles to the leg pieces and between the ends of the leg pieces, the two yoke pieces on one side of the center leg piece of the sheets of odd num-r bered layers comprising the third one of said six patterns and making forty-five angular degree mitre butt joints with said center leg, the two yoke pieces on the other side of the center leg piece of the sheets of the odd numbered layers comprising the fourth one of said six patterns and making ninety angular degree square butt joints with said center leg piece, the two yoke pieces on said other side of the center leg piece of the sheets of the even numbered layers comprising the fifth one of said six patterns which is shorter than said third one of said six patterns while also making forty-five angular degree mitre butt joints with said center leg piece, the two yoke pieces on said one side of the center leg piece of sheets of the even numbered layers comprising the sixth one of said six patterns which is shorter than said fourth one of said six patterns while also making ninety angular degree square butt joints with said center leg piece, the ends of the outer leg pieces of each sheet making forty-five angular degree mitre butt joints with the contiguous ends of the yoke pieces whereby the sheets are unsymmetrical relative to the longitudinal center line of their center leg pieces but a core having the same number of odd and even layers and the same number of sheets per layer is symmetrical relative to such center line and all transversely adjacent butt joints in contiguous layers are offset from each other.

3. A rectangular three-legged laminated magnetic core structure comprising a plurality of fully congruent interleaved lamination layers each formed of at least one sheet of laminations, each said sheet comprising three leg pieces in parallel spaced relation having identical shapes and two differently shaped pairs of yoke pieces connected respectively between opposite ends of the center leg piece and one outer leg piece, the yoke pieces of each said pair being of identical shape, said leg pieces and one pair of said yoke pieces being offset mitered symmetrically at both ends and the other pair of said yoke pieces being offset mitered at one end and square cut at the other end with said square cut ends engaging the same side of the center leg piece in each sheet, the leg and yoke pieces in adjacent layers being offset mitered in opposite directions to provide overlap at all outside corners of said core, alternate layers being formed of identical sheets similarly oriented and the center leg mitres in adjacent layers being relatively oppositely positioned.

References Cited by the Examiner UNITED STATES PATENTS 791,021 5/05 Fortescue 3362=17 X 2,372,074 3/45 Ford 3362l8 X 2,407,626 9/46 Welch 336-217 X 2,896,181 7/59 Zwelling 336-217 3,064,220 11/62 Specht 3362l7 3,069,643 12/62 Stein et al. 336217 JOHN F. BURNS, Primary Examiner. LARAMIE E. ASKIN, Examiner. 

1. A THREE-QUARTER MITRE JOINT MAGNETIC CORE FOR THREEPHASE ELECTRICAL INDUCTION APPARATUS COMPRISING, IN COMBINATION A PLURALITY OF INTERLEAVED FULLY CONGRUENT LAMINATION LAYERS EACH FORMED OF AT LEAST ONE SHEET OF LAMINATIONS, EACH SAID SHEET COMPRISING A CENTER WINDING LEG PIECE, TWO OUTER WINDING LEG PIECES, AND FOUR YOKE PIECES JOINING THE END OF ADJACENT LEG PIECE SO THAT THERE ARE FOUR CORNER JOINTS BETWEEN THE OUTER LEG PIECES AND THE YOKE PIECE AND TWO T-JOINTS EACH COMPRISING TWO JOINTS BETWEEN THE CENTER LEG PIECE AND TWO YOKE PIECES, THE TJOINTS IN THE ODD NUMBERED LAYERS BEING SQUARE BUTT JOINTS WITH THE ADJACENT YOKE PIECE ON SAID SIDE OF THE CENTER LEG AND MITRE BUTT JOINTS WITH THE ADJACENT YOKE PIECE ON THE OTHER SIDE OF THE CENTER LEG, THE T-JOINTS IN THE EVEN NUMBERED LAYERS BEING MITRE BUTT JOINTS WITH THE ADJACENT YOKE PIECE ON SAID ONE SIDE OF THE CENTER LEG AND SQUARE BUTT JOINTS WITH THE ADJACENT YOKE PIECE ON SAID OTHER SIDE OF THE CENTER LEG, ALL OF THE CORNER JOINTS BEING MITRE BUTT JOINTS WHEREBY THREE-QUARTERS OF THE JOINTS IN EACH LAYER AND IN THE CORE AS A WHOLE ARE MITRED AND ALTHOUGHT THE LAYERS ARE UNSYMMETRICAL IN THE REGION OF THEIR T-JOINTS THE CORE AS A WHOLE IS SYMMETRICAL IN THE REGION OF ITS T-JOINTS, THE LEG PIECE OF ONE SET OF ALTERNATE LAYERS ALL BEING REPLICAS OF THE SAME PATTERN, THE LEG PIECES OF THE OTHER SET OF ALTERNATE LAYERS ALL BEING REPLICAS OF A DIFFERENT PATTERN. 